Question: What is PCR?

Ruth Hamill answered on 9 Nov 2015:

PCR is short for polymerase chain reaction. It is a technique invented by Kary Mullis in the 1980’s, who went on to win a Nobel Prize for it. Before its invention, it was a very difficult and time-consuming process to study genes. PCR allows you to make billions of copies of a particular region of the DNA, for example a gene that you think might be associated with a particular trait. It is very precise and targeted and even with miniscule quantities of starting DNA, you can quickly bring it up to a quantity that you can work with directly in the lab. It takes advantage of the natural DNA copying mechanisms of the cell, essentially the DNA is heated to high temperature to open up the strands, the temperature is then reduced to allow the gene to be targeted with short complementary DNA ‘primers’ and then free A’s C’s G’s and T’s bind on to match your DNA and a copy is made, doubling your amount of DNA for that gene. Then the temperature is raised again the 2 strands split again, temperature reduced to allow the bases to bind and the cycle is repeated over and over. PCR is what is termed an exponential process – in about 25 cycles you will get 2 to the power of 25 copies 2 x 2 x 2 x 2 x 2 etc. of the amount of DNA you originally started with… that’s a lot!